Head lice (Pediculus humanus capitis) are parasitic insects that live permanently on humans. Lice occur worldwide and are remarkably widespread in children aged between 3 and 15 years. In many industrialized countries the cases of infested individuals have been observed to increase significantly during the last years. Lice infestations have remained a troublesome problem.
Lice suck blood every few hours. This irritates the skin and infested persons suffer from itching sensations. Children with lice may become sleepless and nervous. Scratching the skin may lead to secondary bacterial infections. The closely related body louse (Pediculus humanus corporis) has the potential to spread serious agents of diseases. Experimental infections and epidemiological studies have revealed that also head lice may act as vectors of bacteria (Robinson D., Leo N., Provic P., Barker S. (2003) Potential role of Pediculus humanus capitis as vectors of Rickettsia prowazeki. Parasitol Res 90:209-211; Sasaki T., Pondel S., Isawa H., Hayashi T., Sekia N., Tomita T., Sawabe K., Kobayashi M., First molecular evidence of Bartonella quintana in Pediculus humanus capitis, collected from Nepalese children. J. Med. Entomol. 43:110-112, (2006)). Parents in concern about their children often undertake enormous efforts to eradicate the parasites.
Traditionally lice have been treated with insecticidal pesticides. Most of the lice-killing chemicals are toxicants acting on the nervous system of insects, e.g. by inhibiting acetylcholinesterases. Insecticides in lice medications are organochlorines, e.g. lindane and DDT, natural pyrethrum or synthetic pyrethroids, e.g. permethrin or resmethrin, often in combination with the monooxygenase inhibitor piperonyl butoxide, the carbamate ester carbaryl, and the thiophosphate ester malathion, and fipronil. Recent patent applications describe topical avermectin (EP2091325A2), 1-N-arylpyrazole and amitraz (US 2009/192207 A1), clothianidin (CN 1011422160 A), spinosad (CN 101305723 A) and also an oral application of ivermectin.
Insecticidal lice products, however, are generally and increasingly thought of with caution, especially when young children are treated with such toxins. Most parents fear to apply to their children harmful insecticidal chemicals. Poisoning does not require ingestion of the product, since anti-lice chemicals readily may be absorbed through the skin.
Nowadays, lice products being free of any insecticides are clearly preferred by parents and many physicians and pharmacists. Medications with lice killing effects based on neurotoxic, immunological, metabolic or other pharmaceutical effects, and this includes the insecticides, are classified as pharmaceutical drugs by EU authorities. The majority of these medications require prescription. By contrast, medicinal products that constitute a growing market, are available over the counter. Medicinal products, however, must only have a physical/mechanical effect on the lice, e.g. kill lice by suffocation.
Home remedies to suffocate lice with various plant oils have been reported to function unreliably, as lice immersed in oils and thereby deprived from oxygen are able to survive up to several hours. Medications containing coconut oil and coconut fatty acid derivates also have been found not to be sufficiently effective.
A suffocation mode of activity has been ascribed to licicidal medications based on silicone/siloxane oils (patents WO 2009/105617, EP 2081428 A, NZ 545068). Cyclomethicone, dimethicone, and other types of silicones and most of them in combination with a plant oil derivative are marketed as non-prescription medicinal products. However, silicone-containing formulations distributed in the hair turned out to be highly flammable. Incidences have occurred, were the entire skin of the head burned away. It is not acceptable to treat a child with a silicone product, which possibly could ruin the live, solely for reason to eliminate a few insects. Silicone medications also have the disadvantages to be very sticky to the hair, and to require, after treatment, several washings with normal shampoo to remove the medication. Some silicone preparations bear even more hazardous risks. DE 102008004676 by Oystershell teaches a formulation of a siloxane in combination with more than 50 weight-percent of saturated linear or branched C10 to C22-carbon chains. If only tiny amounts of this formulation would be inhaled during treatment of the head, it can be deduced from available information on these molecules that the child would suffer serious damages of the lung and possibly even could die.
Herbal preparations are assumed by most people to be in general less harmful than synthetic chemicals, though in some cases this is questionable from a scientific view. Pharmaceutical producers offer lice treatments containing various active ingredients from plants. Many herbal products are based on essential oils, and the modest capacity of essential oils and certain terpenes of the oils to kill insects is known from numerous studies. Several patent applications claim the use of essential oils and terpenes as lice treatments, e.g. limonene (KR 20000022375 and US 2009/176890) or a mixture of essential oils (WO 2008/101131). Also combinations of neem oil and essential oils, e.g. those from anise, tea tree and other Eucalyptus oils and lavender oils have been proposed to treat lice (AU 2008101219). Essential oils, however have the serious disadvantage to be skin irritating and sensitizing. Due to that, the EU legislation 2003/15/EC Directive requires that products containing certain allegedly allergenic essential oil terpenes have to be labelled with a warning note that the product may cause allergies. Several essential oil constituents are skin penetrating neurotoxins, notably anethol from anise or star anise, and commercialized products containing these substances are critical for the health of children. Moreover, due to the pharmaceutical activity of terpenes, these anti-lice products strictly are to be classified as pharmaceutical drugs, not as medicinal products.
For other herbal medications, e.g. based on cassia or carrot seed oil (WO 2008/056365; US 2009/176890, AU 2008101219), none or sparse evidence of their efficacy against lice infestation has been documented in scientific studies.
With nearly all marketed licicidal products the parents are encouraged to use in addition special fine-toothed louse combs to remove remaining and still surviving lice. Hence, producers themselves presume that their medications are not 100% effective. In fact, patients often report that viable lice and/or eggs have survived chemical treatments. Thus, after application of a medicinal treatment, the hair also has to be combed to securely get rid of all lice, which is a very cumbersome and time-consuming procedure not well-tolerated by children.
In consequence, the art continues to seek improvements in better product formulations to combat lice.
Doubtless, there is a strong need for a head lice medication that is highly effective against the parasites, that is safe and easily to use.